Reality check

Discussion on the appropriate carbon factor for grid-supplied electricity has been buzzing in the pages of BSj for months. On 14 August, BSJ teamed up with the UK Green Building Council to host a debate on the subject. It’s a fundamental issue for designers and developers, as the lack of an appropriate figure can distort crucial decisions such as whether to install CHP and trigeneration – one of the keystones of getting planning permission for new commercial developments in the capital.

After the expert presentations, Andy Stanton, who works for Transport for London and is responsible for a number of its buildings, including the head office shared with the London Climate Change Agency (LCCA), got the debate rolling. He said fixed targets for planning set by the LCCA and GLA were useful, if crude, tools to reach the common goal of cutting carbon emissions.

But even those close to the issue find it difficult to get a a handle on the figures. Stanton is working on installation of a sizeable trigeneration system at the Palestra building (BSj 12/06), which is the headquarters of the LCCA. “We’ve had massive difficulty getting clarity on our CO2 figures,” he said. “There is a very great responsibility on us; we are charged with delivering on the Mayor’s climate change action plan and to show what we are doing to reduce energy consumption. All we want is someone to tell us how to do it and give a consistent way to do it.”

Chris Twinn of Arup pointed out that most new buildings are in addition to the current stock. “When we talk about displacement of the present capacity we are getting the wrong end of the stick. We need to look at how we future-proof these buildings ready for reductions in supply rather than the mix of what’s historically been there,” he said. “This brings about very different answers to the question how do you design your building on day one.

“I’m a supporter of carbon trading because it includes a judgement on futures, so do you invest in gas on day one or do you actually start looking at investing in infrastructure for closer generation that might use biomass?” he said.

Another in favour of carbon trading was William Orchard of Orchard and Partners. “The whole calculation changes depending on what you assume is displaced at the margin, whether it’s gas or coal,” he said. ”If we had the proper carbon trading signals those would dictate what was running at the margins.”

Even at the LCCA headquarters, we’ve had massive difficulty getting clarity on our Co2 figures

Andy Stanton, Transport for London

Orchard strongly believes engineers should be taking the lead in determining what carbon factors are used in calculating the CO2 savings that result from CHP. Sue Wolfe of Foreman Roberts disagreed. “The real solution depends on the period over which, and the policy for which, we are designing future plant either as marginal deductions or increases. That is an issue for policy makers whose job it is to look at future generation of electricity.”

Chani Leahong thought the solution might be to use more short-term average figures, based on the next two or three years; these would be closer to reality. But as Roger Hitchin said, most buildings would be there a lot longer.

Orchard opposed use of an average figure for carbon content of grid-supplied electricity. “That includes renewables; as soon as you use an average figure the more renewables you put in the lower the average figure you get and the less renewables you encourage.”

James Thonger of Arup, whose article in BSj (05/07) led to the debate, agreed calculations shouldn’t be based on an average figure. “You should be targeting against a fuel source, not an average. If you take a fuel source you know how well it can be converted for a situation, it therefore takes a lot of debate out of the process. Every single fossil fuel should be used in its most efficient form – that’s how we’re going to get to reductions of 20%.”

So, even among engineers there is no clear consensus on what figures should be used for carbon content of grid-supplied electricity. Until there is, can engineers really make the best decisions on their designs?